Transport213S - Transport in Plants - 1 During the past few...

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Transport in Plants - 1 During the past few weeks, we examined the structure of the “higher” plant body, with occasional references to the functions of plant systems. In the next few days we shall look at how plants are adapted for resource acquisition and to: Maintain water balance and transport water throughout the plant Transport nutrients and solutes to cells and tissues Obtain nutrients for growth and survival from their substrate and from the atmosphere Regulate growth and developmental activities o Chemical signals o Environmental signals Respond to environmental challenges As we look at these subjects, keep in mind how other organisms with which you are more familiar accomplish these same functions. Resource Acquisition Vascular Plant Transport The plant vascular system functions to transport water and minerals throughout the plant. In addition, plant structure and function is optimized for the process of photosynthesis – to efficiently obtain water, CO 2 and light energy in the photosynthetic regions of the plant, primarily leaves, a subject briefly addressed in Biology 211, and reviewed here. Shoot Structure and Light Acquisition As discussed earlier, stems elevate the plant above ground and serve for the attachment of leaves. Phyllotaxy, the arrangement of leaves on the stem, is typically optimized for maximum light capture for photosynthesis, and the typical plant has a spiral phyllotaxy, with leaf primordia placement chemically controlled by the shoot tip meristem.
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Transport in Plants - 2 The leaf area index, the ratio of the upper leaf area to the area of the plant, is one way to measure the plant's ability to capture light energy. Root Structure and Water and Mineral Acquisition In a similar fashion, branching roots, with root tips having root hairs to increase surface area for absorption, maximize the root's ability to take advantage of local resource regions in their substrate. A significant advance in land plants was the co- evolution with mycorrhizae fungi, discussed previously, which increases surface area for resource extraction for both plant and fungus. Transport in Plants Our plant ancestors were aquatic filamentous or laminar (sheet like) organisms whose cells came into contact with their environmental medium, which also supported the plant body. Water and needed nutrients were readily available to individual cells, and little if any differentiation of plant tissues occurred. Migration to land and differentiation of the plant body into tissues and organs required systems to transport needed materials to cells in different parts of the plant from the region where they were obtained. In addition, land plants needed structural support. Both support and conduction are accomplished with secondary vascular tissue in
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Transport213S - Transport in Plants - 1 During the past few...

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